The present invention relates to a heat resistant catalyst sheet, and a process for producing same. More specifically, the present invention relates to a heat resistant catalyst sheet, whose catalytic activity can be retained for a long period of time, because a catalyst component contained therein hardly leaves from the catalyst sheet, and which is superior in its heat resistance and its processability, and relates to a process for producing said heat resistant catalyst sheet. The heat resistant catalyst sheet in accordance with the present invention can be used preferably for, for example, reduction of nitrogen oxides, oxidation of organic substances such as organic solvents, agricultural chemicals and surfactants, and decomposition of dioxin.
As a heat resistant catalyst sheet, JP-B 7-22709 discloses a nitrogen oxide removal catalyst sheet. Said catalyst sheet is obtained by supporting vanadium oxide on solid-carrying paper, which is obtained by impregnating ceramics paper with a mixture of titania sol and silica sol, followed by drying and calcining, wherein said ceramics paper is made from a silica-alumina based ceramics fiber, or an alumina based ceramics fiber.
Further, as another heat resistant catalyst sheets, Japanese Patent No. 2562077 discloses a nitrogen oxide removal catalyst sheet. Said catalyst sheet is obtained by adsorbing and supporting vanadium oxide on solid-carrying paper, which is obtained by impregnating ceramics paper with TiO2 sol, followed by drying and calcining, and further impregnating the resulting paper with SiO2 sol, followed by drying, wherein said ceramics paper is made from a ceramics fiber containing SiO2 sol.
Each of the references referred to above is incorporated herein by reference in its entirety.
However, each of the catalyst sheets disclosed in the above-mentioned publications has problems such that (i) a catalyst component contained therein easily leaves from the catalyst sheet, (ii) its processability is not excellent, and (iii) it does not exhibit enough catalyst performance.
Accordingly, an object of the present invention is to provide a catalyst sheet, whose catalytic activity can be retained for a long period of time, because a catalyst component contained therein hardly leaves from the catalyst sheet, and which is superior in its heat resistance and its processability, and a process for producing said catalyst sheet.
The present inventors have undertaken extensive studies to develop a heat resistant catalyst sheet. As a result, it has been found that a catalyst sheet obtained by combining an aramid fiber and a catalyst component-containing titania fiber can accomplish the object of the present invention, and thereby the present invention has been obtained.
The present invention provides a heat resistant catalyst sheet comprising an aramid fiber and a catalyst component-containing titania fiber.
Further, the present invention provides a process for producing a heat resistant catalyst sheet, which comprises the step of making paper from a mixture of an aramid fiber and a catalyst component-containing titania fiber.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
A catalyst component-containing titania fiber used in the present invention is not particularly limited. As examples of the catalyst component-containing titania fiber, those disclosed in JP-A 11-5036 and Japanese Patent Application No. 10-333786 are enumerated. Each of the references referred to above is incorporated herein by reference in its entirety. Here, the term, xe2x80x9ctitania fiberxe2x80x9d, means a fiber containing a TiO2 component.
Specific examples of the catalyst component-containing titania fiber used in the present invention are those satisfying the following conditions (1) to (7):
(1) titanium oxide is contained in an amount of not less than about 50% by weight, provided that the weight of the catalyst component-containing titania fiber is assigned to be 100% by weight,
(2) a fiber length is not less than about 50 xcexcm, which length is not an average fiber length, but a length of respective fibers,
(3) a fiber diameter is within a range of from about 2 to about 100 xcexcm,
(4) a specific surface area measured by a BET method is not less than about 10 m2/g, and preferably from about 20 to about 300 m2/g,
(5) a pore volume measured by a nitrogen adsorption method is not less than about 0.05 cc/g,
(6) a pore volume having a pore radius of not less than 10 xc3x85 is not less than about 0.02 cc/g, and
(7) a pore radius peak is from about 10 to about 300 xc3x85, and preferably from about.10 to about 100 xc3x85.
A catalyst component used in the present invention is not particularly limited, and may be appropriately determined depending on uses of the catalyst sheet. Examples of the catalyst component usually used are at least one metal selected from the group consisting of V, W, Al, As, Ni, Zr, Mo, Ru, Mg, Ca, Fe, Cr and Pt, at least one metal oxide selected from the group consisting of oxides of said metals, and at least one composite oxide selected from the group consisting of composite oxides of said metals.
When the catalyst sheet in accordance with the present invention is used for reducing nitrogen oxides, it is recommendable to use, as the catalyst component, at least one preferred metal selected from the group consisting of V, W and Mo, or at least one metal oxide selected from the group consisting of oxides of said preferred metals, or at least one composite oxide selected from the group consisting of composite oxides of said preferred metals.
An amount of the catalyst component contained in the catalyst sheet is not particularly limited, and may be determined depending on uses of the catalyst sheet. The amount of the catalyst component is usually from about 0.001 to about 50% by weight in terms of metal oxide, provided that said metal contained in the catalyst sheet is converted into its metal oxide, and the weight of the catalyst component-containing titania fiber is assigned to be 100% by weight.
A process for producing the catalyst component-containing titania fiber is not particularly limited. As examples of the production process thereof, those comprising steps mentioned in the following Process-1 and Process-2 are enumerated. It is necessary to carry out respective steps of from Step-1 to Step-4, through which a precursor fiber is obtained, under atmosphere of an inert gas such as nitrogen gas. However, the obtained fiber precursor can be handled in the air.
Process-1
Step-1 of dissolving a titanium alkoxide in an alcohol such as isopropyl alcohol to obtain a solution,
Step-2 of hydrolyzing the obtained solution to obtain a slurry,
Step-3 of dissolving a vanadium compound in the slurry to obtain a spinning solution,
Step-4 of spinning the spinning solution to obtain a precursor fiber, and
Step-5 of calcining the precursor fiber to obtain a titania fiber.
Process-2
Step-1 of dissolving a titanium alkoxide and a vanadium compound in an alcohol such as isopropyl alcohol,
Step-2 of hydrolyzing the obtained solution to obtaining a slurry,
Step-3 of adding a solvent to the slurry, followed by mixing, and then further adding a silica compound thereto to obtain a spinning solution,
Step-4 of spinning the spinning solution to obtain a precursor fiber, and
Step-5 of calcining the precursor fiber to obtain a titania fiber.
A unit weight of the catalyst component-containing titania fiber present in the catalyst sheet in accordance with the present invention is not particularly limited, and may be determined depending on uses of the catalyst sheet. Here, the term, xe2x80x9cunit weightxe2x80x9d, means a weight of the catalyst component -containing titania fiber per unit area of the sheet. From a viewpoint of increasing catalyst performance and permeability of the obtained catalyst sheet, a preferred unit weight of the catalyst component-containing titania fiber is from about 5 to about 900 g/m2.
The term, xe2x80x9caramid fiberxe2x80x9d, used in the present invention means an aromatic polyamide fiber, namely, a fiber of polyamide having both aromatic nucleuses and amide bonds in its main molecular chain. The aramid fiber is not particularly limited. Examples of the aramid fiber are a para type aramid fiber and a meta type aramid fiber. Of these, the para type aramid fiber is preferred. From a viewpoint of easy formation of a sheet from the aramid fiber using no binder, an aramid fiber comprising a fibrillated fiber is preferable. Accordingly, a fibrillated para type aramid fiber is particularly preferable. Incidentally, the aramid fiber used in the present invention may be those comprising a fibrillated aramid fiber and a non-fibrillated aramid fiber.
Examples of the para type aramid fiber are a fiber of trademark TWARON, manufactured by Nippon Aramid Co., LTD., a fiber of trademark KEVLAR, manufactured by Dupont Co., and a fiber of trademark TECHNORA, manufactured by Teijin Limited. Examples of the meta type aramid fiber are a fiber of trademark NOMEX, manufactured by Dupont Co., a fiber of trademark TEIJIN CONEX, manufactured by Teijin Limited, and a fiber of trademark APYEIL, manufactured by Unitika Ltd.
A unit weight of the aramid fiber present in the catalyst sheet in accordance with the present invention is not particularly limited, and may be determined depending on uses of the catalyst sheet. Here, the term, xe2x80x9cunit weightxe2x80x9d, means a weight of the aramid fiber per unit area of the sheet. From a viewpoint of balance among catalyst component-retaining ability, sheet strength and permeability of the catalyst sheet obtained, a preferred unit weight of the aramid fiber is from about 5 to about 900 g/m2.
A process for producing the heat resistant catalyst sheet in accordance with the present invention is not particularly limited. An example of said production process is a process comprising the step of making paper from a mixture of an aramid fiber and a catalyst component-containing titania fiber. From a viewpoint of preventing the catalyst component from eluting out of the catalyst component-containing titania fiber, a preferable production process of the catalyst sheet is a process, which comprises the step of making paper from a mixture of an aramid fiber and a catalyst component-containing titania fiber, in the presence of at least one surfactant selected from the group consisting of alkyl dimethylaminoacetate betaines represented by the following formula (I), alkylamine acetates represented by the following formula (II) and amines represented by the following formula (III): 
wherein R1 is a C8-C22 alkyl group, 
wherein R2 is a C8-C22 alkyl group, and 
wherein X is a hydrogen atom or a methyl group, Y is a hydrogen atom or a methyl group, and R3 is a C8-C22 alkyl group.
Particularly preferred surfactants are lauryl dimethylaminoacetate betain, tridecyl dimethylaminoacetate betain and myristyl dimethylaminoacetate betain, which are represented by the formula (I); laurylamine acetate, tridecylamine acetate and myristylamine acetate, which are represented by the formula (II); and lauryl-dimethylamine, tridecyl-dimethylamine and myristyl-dimethylamine, which are represented by the formula (III).
How to make paper from a mixture of an aramid fiber and a catalyst component-containing titania fiber is not particularly limited. For example, a process comprising the following steps 1 to 3 can be given.
Step-1 of placing water, a pulpified aramid fiber, a surfactant and a catalyst component-containing titania fiber in this order in a pulp disaggregating machine, and mixing them under stirring to obtain a uniform mixture,
Step-2 of making wet paper from the above-mentioned uniform mixture using a paper-making machine, and
Step-3 of dehydrating and drying the wet paper to obtain a catalyst sheet.
In the above Step-1, it is usually recommendable to carry out the stirring under conditions of making a length of the catalyst component-containing titania fiber not less than about 10 xcexcm. In this step, if desired, a defoaming agent such as polyether type deforming agents, ester of fatty acid type defoaming agents and silicone type defoaming agents may be used. Additionally, in this step, an organic binding agent, which disappears during drying of Step-3 mentioned above, may be used to improve handling of the wet paper mentioned in the above Step-2, and to improve handling of the obtained catalyst sheet at a time of its transportation or installation.
In the above Step-3, conditions of dehydrating and drying are not particularly limited. Step-3 may be carried out under conventional conditions using an apparatus known in the art. Drying may be carried out two or more times, wherein temperature may be different from one another. In addition, drying may be carried out after installing the heat resistant catalyst sheet in, for example, a reaction apparatus for reducing nitrogen oxides.
The heat resistant catalyst sheet in accordance with the present invention comprises a catalyst component-containing titania fiber and an aramid fiber. Its catalytic activity can be retained for a long period of time, because a catalyst component therein hardly leaves from the catalyst sheet. The present catalyst sheet usually has a heat resistance of at least 100 hour use at 200xc2x0 C., and superior processability, and is capable of retaining for a long period of time its catalytic activity for, for example, reducing nitrogen oxides, oxidizing organic substances such as organic solvents, agricultural chemicals and surfactants and decomposing dioxin. Thus, it can be said that its utility value is great from an industrial point of view.